He said: "The message is loud and clear - King Newt's days are numbered."

In a further comment that will likely provoke Ken Livingstone - and do little to reassure those who think Boris is a comical candidate - Mr Johnson said the job of mayor of London was "simple".

He said: "The job of the mayor is simple - to get people to work on time, to ensure people feel safe on the streets, to help people find a place to call home, to celebrate our diversity and to champion our success".

Tory leader David Cameron said Mr Johnson would be an excellent candidate in next year's mayoral election.

Mr Cameron said: "I know the party will unite behind him to remove Ken Livingstone from office. It's about time that all Londoners had the chance to vote for real change."

Mr Livingstone vowed to challenge his cycling opponent and run on his record of building public services, neighbourhood policing teams, record transport investment, the 2012 Olympics and climate change.

The mayor said: "Boris Johnson proposes to add a lack of managerial competence to the Thatcherite decline and division always represented by London's Tories.

"He opposed congestion charging and then did a u-turn on this, supported the anti-lesbian and gay Section 28 and then abandoned this, says he is green but opposed the Kyoto Treaty."

Mr Livingstone added: "In addition to damaging mistakes he has made policy on the hoof - proposing a totally wrong system of bus contracts for London and coming out against the requirement that 50 per cent of new housing should be affordable."

Mr Johnson, who enjoys a high media profile thanks to his journalism work and appearances on Have I Got News For You, won the candidature after a London-wide primary open to all residents.

The 43-year-old former shadow minister for higher education secured 15,661 of the 20,019 total votes cast.